Method for the production of easily wetted, water-soluble, powdered at least alkylated non-ionic cellulose ethers

ABSTRACT

The invention relates to a method for the production of at least alkylated, non-ionic cellulose ethers, whereby at least 10% of all hydroxy groups contained therein are alkylated and which may flocculate in water, within a temperature range of 45 to 95° C. The invention is characterized in that at least one surfactant in solid, liquid, or solution form is added to the cellulose for production of the cellulose ether.

The present invention relates to a process for preparing water-soluble,pulverulent, at least alkylated, nonionic cellulose ethers which arepreferably coagulable in water having a temperature in the range from 35to 95° C. and are modified with surfactants before conversion of thecellulose to the cellulose ether in such a manner that, owing to theimproved wettability, substantially lump-free stir-in of the celluloseether in cold water results.

The preparation of cellulose ethers having uniform or differentsubstituents is known (see, for example, Ullmann's Enzyklopädie derTechnischen Chemie, Vol. 9, “Celluloseether”, Verlag Chemie, Weinheim,4th edition 1975, p. 192ff; K. Engelskirchen: “Polysaccharid-Derivate”in Houben Weyl, Vol. E 20/III, 4th ed., Georg Thieme Verlag Stuttgart,1987, p. 2042 ff).

To prepare these cellulose ethers, for example methylcellulose,methylhydroxyethylcellulose, methylhydroxypropylcellulose andethylhydroxyethylcellulose, the starting material, the cellulose, isinitially milled to increase the surface area and the resulting particlesize should generally be less than 2.5 mm, if possible even less than 1mm. The resulting, voluminous cellulose powder is converted by additionof base, for example NaOH, KOH, LiOH and/or NH₄OH, in solid or liquidform, to the alkali metal cellulose. This is followed, with or withoutisolation of the alkali metal cellulose, by a one- or multistage,continuous or batchwise, etherification with the appropriate reagents.The resulting cellulose ethers are purified using water or suitablesolvent mixtures in a known manner to remove the reaction by-products,dried and milled and optionally admixed with other components.

Despite the good solubility of alkylated cellulose ethers in cold water,the preparation of aqueous solutions of them frequently presents aproblem. This is true in particular when the cellulose ether is a finepowder having increased surface area because rapid viscosity developmentis desired. When such a fine cellulose ether powder comes into contactwith water, the individual particles swell and accumulate to formrelatively large agglomerates whose surface area is coagulated in agel-like manner. However, depending on the mixing intensity, there is acertain proportion of completely unwetted cellulose ether in theinterior of these agglomerates. Depending on the viscosity of theresulting solution and the average polymer chain length, completedissolution of these agglomerates in the case of highly viscous productsmay take up to 24 hours.

In order to minimize the problem described which occurs in preparingaqueous solutions of cellulose ethers, various solutions have beensuggested:

The cellulose ether powder can be sprinkled into water at a temperatureabove the coagulation point of the corresponding cellulose ether andthen cooled gradually. The cellulose ether then distributes evenly inthe water without forming lumps before it gradually goes into solutionas the temperature falls. However, such a process is time-intensive andrequires an apparatus to heat the water.

When direct stir-in of the cellulose ether in cold water without lumpingis desired, glyoxal, for example, can be used in preparing the celluloseether to obtain partial, reversible crosslinking which leads to theformation of hemiacetals having free hydroxyl groups of the celluloseether. On dissolution in neutral or weakly acidic water, the hemiacetalis cleaved after a time delay and a sharp viscosity increase withoutlumping occurs only after distribution of the powder in the aqueousmedium. The length of the time delay can be adjusted quite precisely viathe degree of crosslinking. However, disadvantages of this variant arethe additional working step in preparing the cellulose ether, i.e. thecrosslinking, and also the time-delayed viscosity increase.

A further possibility for improving the stir-in of cellulose ethers incold water is to treat them with surfactants which contain lauroylradicals. In this process described in U.S. Pat. No. 2,647,064 and U.S.Pat. No. 2,720,464, cellulose ethers are treated with surfactants inaqueous suspension at a temperature above the coagulation point of thecellulose ether, so that the resulting products contain surfactantsadsorbed on the surface which results in improved stir-in. The materialmay be treated with surfactants either in the course of aqueous workupto free it of reaction by-products and salt or by redispersion ofcellulose ethers in hot aqueous systems at a temperature above thecoagulation point of the cellulose ether. Spraying of the surfactantonto the damp cellulose ether during the centrifugation which serves toremove the aqueous medium from the cellulose ether is also disclosed.However, a considerable disadvantage of the process described is thenecessary use of excess surfactant in the hot aqueous suspension of thecellulose ether. Only a small portion of the surfactant used is adsorbedon the cellulose ether. According to the examples of U.S. Pat. No.2,720,464, this proportion is only from 3 to 6%. Since it cannot bedisposed of with the washing water and also for reasons of cost, thesubstantial proportion of the nonadsorbed surfactant has to be recycledor recovered. Furthermore, the hot, aqueous surfactant solution foamsvery vigorously while the cellulose ether is removed. In addition, anopportunity has to be found in the process for adding and mixing themixture of surfactant and water at a point in time at which in generalno reagent is added.

WO 99/47249 discloses the achievement of improved dispersibility andwettability of hydrocolloids by dry admixing of surfactants withmaterial heated to above its melting point. As well as the additionalapparatus demands for such a process, the even distribution of smallamounts of surfactant is problematic.

In JP-A-11/322 801, glycols and/or nonionic surfactants having HLBvalues of from 3 to 17 are sprayed onto cellulose ethers in order toimprove the stir-in of the cellulose ethers. HLB means “hydrophiliclipophilic balance” and is a measure for the polarity of the surfactantsand their ability to form oil-in-water or water-in-oil emulsions.

In CN-A-1 149 643, polyanionic cellulose ethers, for examplecarboxymethyl-cellulose, are prepared by alkalizing cellulose using abase solution containing a surfactant, and etherifying, aftertreatingand spinning it.

JP-B-89/038 403 describes the use of different surfactants in amounts offrom 0.1 to 10% in preparing hydroxyethylcellulose in organic solvents,in particular isopropanol and tert-butanol. In comparison to productswhich have been prepared without the addition of surfactants, theresulting products show an improved clear solubility.

It is an object of the present invention to provide a process forpreparing at least alkylated, nonionic cellulose ethers which arepreferably coagulable in water having a temperature in the range from 35to 95° C. and delivers products which are notable for their improvedwetting and stir-in behavior in cold, aqueous solutions. The processshall not have the disadvantages of the prior art, require no additionalaggregates or process steps and guarantee the purification of theproducts to remove reaction by-products and salts by washing with anexcess of water at a temperature above the coagulation point of thecellulose ether, but below 100° C.

This object is achieved by the addition before conversion to thecellulose ether of at least one surfactant to the cellulose in thecourse of metering in the reactants required for the preparation of thecellulose ether.

The present invention accordingly provides a process for preparing atleast alkylated, nonionic cellulose ethers in which at least 10% of allhydroxyl groups are alkylated and which are coagulable in water in atemperature range of from 45 to 95° C., preferably from 50 to 95° C. andmore preferably from 65 to 95° C., and are converted to the celluloseether by

-   a) activating the cellulose by alkalization in the presence of    water, base and organic dispersing auxiliary,-   b) etherifying the activated cellulose in a one- or multistage    process using an etherifying agent by a Williamson ether synthesis    and-   c) purifying the product in a subsequent purification step by    washing with water which has a temperature above the coagulation    point of the cellulose ether to remove reaction by-products and    salts, which comprises adding at least one surfactant in solid,    liquid and/or dissolved form before the cellulose is converted to    the cellulose ether.

For the purposes of the present invention, coagulability means that atleast 90% by weight of the cellulose ether is insoluble in water at agiven temperature.

The cellulose ethers prepared according to the invention have animproved wettability and accordingly have a lower tendency to form lumpswhen preparing aqueous solutions.

It has been found to be unimportant whether the surfactant is metered inas an aqueous solution or in a solution or dispersion together with theorganic dispersing auxiliary used. The surfactant used is completely andevenly adsorbed by the cellulose, irrespective of the type of surfactantused. The effect is equally marked for anionic surfactants and forneutral or cationic surfactants, and equally for surfactants having highHLB values and surfactants having low HLB values, irrespective of theprecise structure.

Surprisingly, it has been found that in spite of the very goodsolubility and complete miscibility with water of the surfactants used,they remain completely in the product even after conversion to thecellulose ether, even though it would have been expected that theaqueous workup to remove the reaction by-products, salts and dispersingauxiliaries at elevated temperature and large water excess (parts byweight ratio from 5:1 to 100:1, based on the cellulose ether) would leadto the surfactants being washed out at least virtually completely.Accordingly, no surfactant could be detected in the washing water usedfor the washing.

With respect to wettability and lump-free stir-in, the cellulose ethersprepared according to the invention have similar properties atcomparable surfactant doping to the cellulose ethers which, according tothe processes of JP-A-11/322 801, U.S. Pat. No. 2,647,064 and U.S. Pat.No. 2,720,464, have been treated with surfactants only after conversionto the cellulose ether. However, the process according to the inventiondoes not have the disadvantages of the prior art, in particular the highsurfactant loss of the processes described in the American patents.

The maximum ratio of organic dispersing auxiliary used to cellulose ispreferably 25:1, more preferably 15:1.

Useful organic dispersing auxiliaries include all dispersing auxiliariesdisclosed by the literature for this application purpose, but preferablyaliphatic and cyclic ethers, for example dimethyl ether, diethyl ether,dibutyl ether, dimethoxyethane, 1,4-dioxane or tetrahydrofuran.

The maximum water content in the reactant mixture during alkalizationshould preferably be 25 molar equivalents, more preferably 15 molarequivalents, based on the amount of cellulose used, and in particular bein the range from 2 to 5 molar equivalents.

A maximum of 20% by weight, preferably a maximum of 10% by weight andmore preferably a maximum of 1% by weight, of surfactant, based on theamount of cellulose used, are added. Surprisingly, it was found that theuse of even small surfactant amounts of about 0.01% by weight, based onthe amount of cellulose used, have an effect with regard to the rapidityand evenness of viscosity development on stir-in in cold water. It isequally surprising that the use of a surfactant quantity of from about1% by weight, based on the amount of cellulose used, has a virtuallymaximum effect with regard to the rapidity and evenness of viscositydevelopment on stir-in in cold water. The surfactant is generally addedbefore the base is added.

Preference is given to metering in the surfactant in the form of anaqueous solution of any desired concentration. Furthermore, it is alsoconceivable to add the surfactant in solid or liquid form to the organicdispersing auxiliary or to meter it directly into the mixture.

Preference is given to using surfactants whose wetting ability by DIN53901 at 20° C. is less than 10 g of active substance/l, preferably lessthan 5 g of active substance/l and more preferably less than 2 g ofactive substance/l. Furthermore, particular preference is given to usingthose surfactants which reduce the surface tension of aqueous solutionsby at least 20%.

Particular preference is given to using anionic surfactants, for examplephosphoric acid mono- and diesters having long-chain, branchedalkylpolyethylene glycol ether groups, sulfates, for example sodiumdodecyl sulfate or sodium cetyl stearyl sulfate, alkylphenol polyglycolether sulfates, sorbitan oleates, alkanesulfonates, cationicsurfactants, for example coconut alkyldimethylbenzylammonium chloride ordicoconut dimethylammonium chloride, neutral surfactants, for examplepolyether-modified polysiloxanes or alkylphenol polyglycol ethers, andalso betaines, for example fatty acid amidoalkyl betaine orN,N-distearyl-N-methyl-N-(3-sulfopropyl)ammonium betaine.

The cellulose ethers prepared according to the invention can be stirredinto cold water without lumps when the mixing energy is sufficient. Whenthe mixing energy is insufficient, a lower degree of lumping occurs andaccordingly a more rapid and more even viscosity development, as is thecase in products which have been converted to the cellulose etherwithout the use of surfactants. This statement applies in particular tothe case of very finely divided products where more than 90% of allparticles have a diameter of less than 180 μm.

The process according to the invention is further described hereinbelowusing examples without being restricted thereby:

EXAMPLES NO. 1 to 3, 5 TO 17 AND 18 (COMPARATIVE)

Preparation of the Cellulose Ethers without the Addition of Surfactants

In a reactor having a horizontal mixing shaft, 100 parts by weight of awood pulp a, b or c (ground to 0.5 mm) in 350 parts of dimethoxyethaneare admixed with such an additional quantity of water and 58.3 parts ofa 49.3% sodium hydroxide solution that the total water content in themixture of the reactants after addition of the sodium hydroxide solutionis 42.05 parts, based on the cellulose. After the addition of the sodiumhydroxide solution, the cellulose is alkalized for an appropriate periodof time, in general from 30 minutes to 2 hours, at a suitabletemperature and then reacted at from 60 to 80° C. with a sufficientquantity of ethylene oxide to obtain the appropriate degree ofhydroxyethyl substitution (MS). A second portion of 49.3% sodiumhydroxide solution and then the amount of methyl chloride whichcorresponds to the sum of the molar equivalent amounts of both sodiumhydroxide portions, based on the amount of cellulose used, are thenadded and the reaction continues at from 90 to 100° C. until theappropriate degree of methyl group substitution is attained.

After the end of the reaction, the organic dispersing auxiliary isdistilled out of the reaction mixture under reduced pressure and theresulting crude product is washed with hot water of a temperature abovethe coagulating point of the corresponding cellulose ether until thematerial has been completely purified to remove reaction by-products andthe salt content is below 1%. However, a total of at least 10 times thequantity of water is used for washing the cellulose ether with boilingwater.

The resulting crude products are then further treated as follows:

EXAMPLE NO. 1, 12 AND 17 (COMPARATIVE)

Preparation Variant A (Without Addition of Surfactant)

The resulting crude products without the addition of surfactant aredried, ground, sieved and backmixed to the desired particle sizedistribution. The particle size distribution of the products tested isas follows: 75%<63 μm, 20% from 63 to 100 μm and 5% from 100 to 125 μm.

EXAMPLE NO. 2, 3, 5 TO 11, 13 AND 18 (COMPARATIVE)

Preparation B: Admixing of Surfactant to the Crude Product Analogous toU.S. Pat. No. 2,720,464, Column 6, Lines 34 to 39

100 g of crude product (absolutely dry, i.e. corrected for moisture) areintimately kneaded for 30 minutes with 5 g of a solution or suspensionof surfactant in water corresponding to the weight ratios of surfactantstated in the tables, based on the cellulose ether (absolutely dry),dried, ground, sieved and backmixed to the desired particle sizedistribution.

EXAMPLE NO. 4, 14 to 16 AND 19

Preparation Variant C: Preparation of Cellulose Ethers using Surfactants(Process According to the Invention)

The same procedure as described for the preparation of the celluloseethers without the addition of surfactants is carried out, except thatthe appropriate quantity of surfactant in percent by weight, based onthe amount of cellulose used, is added to the reactant mixture inaqueous solution or suspension before addition of the sodium hydroxidesolution.

Surfactant amounts used:

Example No. Surfactant Amount used [parts by weight] 4 A 0.2 14 D 0.2 15G 0.2 16 A 1.0 19 A 0.2

The crude product resulting from the reaction is treated as describedabove for preparation variant A.

The viscosity development when the cellulose ether is dissolved, whichcorrelates directly with the extent of lumping, is recorded in aBrabender viscometer at 20° C. in the following manner:

The cellulose ethers are used as a very fine powder having the followingparticle size distribution: 75% having a particle size of <63 μm, 20%having a particle size of from 63 to 100 μm and 5% having a particlesize of from 100 to 125 μm. Depending on the achievable end viscosity,an appropriate amount of cellulose ether is intimately mixed in a vesselfor 10 seconds with the appropriate amount of water to a final weight of430 g with stirring using an Ultra-Turrax® at 8 000 rpm. The water has atemperature of 20+/−1° C. The solution is then transferred in the courseof a maximum of 5 seconds to a viscometer from Brabender and themeasurement is started. The viscosity development in [BE] (Brabenderunits) which is directly proportional to the corresponding viscosity inmPas (according to Brookfield) is recorded with the support of softwarefor a maximum of 3 hours and evaluated.

Tables 1 and 3 make clear that for the tendency to lump and theresulting viscosity development of cellulose ethers on stir-in in coldwater, it is unimportant whether the surfactant in the form of asolution is intimately mixed with the damp cellulose ether (examples 3and 18 in analogy to U.S. Pat. No. 2,720,464, column 6, lines 34 to 39)or added directly to the reactant mixture before the conversion to thecellulose ether (examples 4 and 19).

TABLE 1 Viscosity development/dissolution behavior in the Brabenderviscometer at 20° C. Material: methylhydroxyethylcellulose based on woodpulp a; viscosity: 39 000 mPas (1.9%, absolutely dry, measured using aBrookfield RVT viscometer); weight 3 g (absolutely dry) Amount ofTheoretical 20% 50% Ex. Sur- surfactant Preparation end viscosity¹⁾ EV²⁾EV²⁾ No. factant used [%] variant [BE] [min] [min] 1 — — A 795 17 — 2 A0.01 B 795 5.5 — 3 A 0.2 B 795 1 4.5 4 A 0.2 C 795 1 4.5 5 A 1.0 B 7950.5 1 6 A 5.0 B 795 0.5 1 7 B 0.2 B 795 0.5 4 8 C 0.2 B 795 0.5 2 9 D0.2 B 795 0.5 4 10 E 0.2 B 795 0.5 2 11 F 0.2 B 795 0.5 2.5¹⁾theoretical achievable viscosity under the conditions selected inBrabender units [BE] on complete dissolution of the cellulose ether²⁾time in minutes until achievement of 20 or 50% of the achievable endviscosity in [BE]; a dash in the table means that the appropriateviscosity level was not attained owing to comparatively extensivelumping even after a measuring time of 180 minutes

-   Surfactant A: anionic surfactant: sodium 2-ethylhexylsulfonate;    solubility in water: 300 g/l-   Surfactant B: anionic surfactant: sodium dialkyl sulfosuccinate;    soluble in water-   Surfactant C: cationic surfactant: dicoconut dimethylammonium    chloride; soluble in water-   Surfactant D: neutral surfactant: EO/PO block polymer; soluble in    water-   Surfactant E: neutral surfactant: nonylphenol polyglycol ether;    soluble in water-   Surfactant F: betaine:    N,N-distearyl-N-methyl-N-(3-sulfopropyl)ammonium betaine; solubility    in water: <10 g/l

TABLE 2 Viscosity development/solubility behavior in Brabenderviscometer at 20° C. Material: methylhydroxyethylcellulose based on woodpulp b; viscosity 23 000 mPas (1.9%, absolutely dry, measured with aBrookfield viscometer); weight 4.3 g (absolutely dry) Amount ofTheoretical 20% 50% Ex. Sur- surfactant Preparation end viscosity. EV EVNo. factant used [%] variant [BE] [min] [min] 12 — — A 1000 4 — 13 A 0.2B 1000 1 3 14 D 0.2 C 1000 <0.5 1 15 G 0.2 C 1000 1 2 16 A 1.0 C 1000<0.1 0.5

Surfactant G: cationic surfactant: coconut alkyldimethylbenzylammoniumchloride; soluble in water

TABLE 3 Viscosity development/solubility behavior in a Brabenderviscometer at 20° C. Material: methylhydroxyethylcellulose based on woodpulp c; viscosity 5 000 mPas (1.9%, absolutely dry, measured with aBrookfield viscometer); weight 5.0 g (absolutely dry) Theoretical Amountof Prepa- end 20% 50% 80% Ex. Sur- surfactant ration viscosity EV EV EVNo. factant used [%] variant [BE] [min] [min] [min] 17 — — A 700 1.5 56— 18 A 0.2 B 700 0.5 1 1.5 19 A 0.2 C 700 <0.3 0.5 1

In comparison to table 1, tables 2 and 3 show that when the particlesize distribution and mixing energy introduced are identical, the degreeof lumping and accordingly also the viscosity development depend on theaverage polymer chain length. Cellulose ethers having relatively shortaverage polymer chain lengths dissolve more quickly and more evenly, andaccordingly, when the mixing energy is insufficient and partial lumpingoccurs, have a more even viscosity development than cellulose ethershaving relatively long average polymer chain lengths.

However, irrespective of the end viscosity, improved wetting andlump-free stir-in behavior is observed once surfactants are added to thereactant mixture to be alkalized.

1. A process for preparing an alkylated, nonionic cellulose etherproduct comprising: a) activating cellulose by alkalization in thepresence of water, base and organic dispersing auxiliary to provideactivated cellulose in a reaction mixture by adding at least onesurfactant to the reaction mixture, such that the at least onesurfactant is added to the reaction mixture prior to addition or thebase into the reaction mixture; b) etherifying the activated celluloseusing an etherifying agent by a Williamson ether synthesis to provideetherified cellulose; and, c) purifying the etherified cellulose bywashing with water at a temperature above the coagulation point of theetherified cellulose to remove reaction by-products and salts to providesaid cellulose ether product; wherein at least 10% of all hydroxylgroups are alkylated, and which cellulose ether product is coagulable inwater in a temperature range of from 45 to 95° C.
 2. The process asclaimed in claim 1, wherein a maximum ratio of organic dispersingauxiliary to cellulose is 25:1.
 3. The process as claimed in claim 1,wherein a maximum water content in the reactant mixture during thealkalization is 25 molar equivalents, based on the amount of celluloseused.
 4. The process as claimed in claim 1, wherein a maximum of 20% byweight of surfactant, based on the amount of cellulose used, isintroduced before addition of the base to the reaction mixture.
 5. Theprocess of claim 1, wherein the surfactant comprises a wetting abilityas measured by DIN 53901 at 20° C. of less than 10 g of activesubstance/I.
 6. The process of claim 1 wherein the at least onesurfactant is in solid, liquid and/or dissolved form.
 7. The process ofclaim 1 wherein the etherifying step occurs in a single stage ormultistage process.
 8. The process of claim 1 wherein the at least onesurfactant comprises an anionic surfactant.
 9. The process of claim 1wherein the organic dispersing auxiliary is selected from the groupconsisting of aliphatic and cyclic ethers.
 10. The process of claim 1wherein the at least one surfactant comprises from 0.01 to 1.0 weightpercent based on the amount of cellulose in the reaction mixture. 11.The process of claim 1 in which at least 10% of all cellulose hydroxylgroups are alkylated and converted to a cellulose ether product which iscoagulable in water in a temperature range of from 45 to 95° C.
 12. Theprocess of claim 1 wherein the organic dispersing auxiliary comprises analiphatic ether or cyclic ether.
 13. The process of claim 1 wherein theorganic dispersing auxiliary comprises dimethyl ether, diethyl ether,dibutyl ether, dimethoxyethane, 1,4-dioxane or tetrahydrofuran.
 14. Theprocess of claim 1 wherein the base comprises NaOH, KOH, LiOH and/orNH₄OH.
 15. The process of claim 1, wherein the non-ionic cellulose etherproduct further comprises oxalkylated hydroxyl groups.
 16. The processof claim 1, wherein the non-ionic cellulose ether product is a methylhydroxyethyl cellulose, a methyl hydroxypropyl cellulose or an ethylhydroxyethyl cellulose.
 17. A process for preparing an alkylated,nonionic cellulose ether product comprising: a) activating cellulose byalkalization in the presence of water, base and organic dispersingauxiliary to provide activated cellulose in a reaction mixture by addingfrom 0.01 to 1.0 weight percent based on the cellulose of at least onesurfactant to the reaction mixture, such that the at least onesurfactant is added to the reaction mixture prior to addition of thebase into the reaction mixture; b) etherifying the activated celluloseusing an etherifying agent by a Williamson ether synthesis to provideetherified cellulose; and, c) purifying the etherified cellulose bywashing with water at a temperature above the coagulation point of theetherified cellulose to remove reaction by-products and salts to providesaid cellulose ether product; wherein at least 10% of all hydroxylgroups are alkylated, and which cellulose ether product is coagulable inwater in a temperature range of from 45 to 95° C.
 18. The process ofclaim 17 wherein the surfactant is selected from the group consisting ofphosphoric acid mono- and diesters having long-chain branchedalkylpolyethylene glycol ether groups, sodium dodecyl sulfate, sodiumcetyl stearyl sulfate, alkylphenol polyglycol ether sulfates, sorbitanolcates, alkanesulfonates, coconut alkyldimethylbenzylammonium chloride,dicoconut dimethylammonium chloride, polyether-modified polysiloxanes,alkylphenol polyglycol ethers, fatty acid amidoalkyl betaine,N,N-distearyl-N-methyl-N-(3-sulfopropyl)ammonium betaine, and mixturesthereof.
 19. The process of claim 17 wherein the organic dispersingauxiliary comprises an adiphatic ether or cycile ether.